System and method of providing group dispatch calling between users in distinct geographical areas

ABSTRACT

A dispatch communications system is disclosed that facilitates group dispatch communications respectively between subscriber units residing within a first geographical area, subscriber units residing within a second geographical area, and subscriber units residing respectively within the first and second geographical areas. The dispatch communications system includes a first intra-area dispatch communications network to facilitate group dispatch calling between subscriber units residing within a first geographical area; a second intra-area dispatch communications network to facilitate group dispatch calling between subscriber units residing within a second geographical area different than the first geographical area; and an inter-area dispatch communications network to facilitate group dispatch calling between subscriber units residing respectively within the first and second geographical areas. A call processing unit controls both inter-area and intra-area group dispatch calls for the dispatch communications system.

FIELD OF THE INVENTION

This invention relates generally to communications systems, and inparticular, to a system and method of providing group dispatch callingbetween users in distinct geographical areas.

BACKGROUND OF THE INVENTION

Group dispatch calling between users is becoming increasingly popular.One of the main reasons for its popularity is that the setup time for agroup dispatch call is relatively small as compared to, for example, thesetup time for a group cellular telephone call (i.e., a conferencecall). Another distinction between a dispatch communication and acellular telephone communication is that a dispatch communication istypically half-duplex. That is, a dispatch communication link isallocated to a single user at a time for transmitting voice and/or data.

In the past, group dispatch calling (a dispatch call between a callingparty and two or more target parties) was limited to users situatedwithin a limited geographical area, such as, for example, Chicago. Thereason is that the dispatch communications network processing groupdispatch calls had limited coverage within such geographical area. Thus,if a user roamed beyond the geographical area covered by thecorresponding dispatch communications network, for example, to LosAngeles, the user would not be able to make group dispatch calls.

Accordingly, there is a need for a system and method of providing groupdispatch calling between users in distinct geographical areas coveredrespectively by distinct intra-area dispatch communications networks.

SUMMARY OF THE INVENTION

An aspect of the invention relates to a dispatch communications systemthat facilitates group dispatch communications between subscriber unitsresiding within a first geographical area, subscriber units residingwithin a second geographical area, and subscriber units residingrespectively within the first and second geographical areas. Thedispatch communications system includes a first intra-area dispatchcommunications network to facilitate group dispatch calling betweensubscriber units residing within a first geographical area; a secondintra-area dispatch communications network to facilitate group dispatchcalling between subscriber units residing within a second geographicalarea different than the first geographical area; and an inter-areadispatch communications network to facilitate group dispatch callingbetween subscriber units residing respectively within the first andsecond geographical areas.

Another aspect of the invention relates to a call processing unit, suchas a visitor location registration dispatch (VLR-D) device, to processinter-area and intra-area group dispatch calls for the dispatchcommunications system. In this regard, the call processing unit receivesa group dispatch call request from a calling subscriber unit requestinga dispatch call to two or more target subscriber units, and establishesa communications link across the intra-area communications network if atleast one of the target subscriber units is located within the samegeographical area as the calling subscriber unit, and/or across theinter-area communications network if at least one of the targetsubscriber units is located a different geographical area as that of thecalling subscriber unit.

Another aspect of the invention relates to an exemplary call processingmethodology implemented by the call processing unit. According to thecall processing methodology, the call processing unit receives a groupdispatch call request from a calling subscriber unit targeting aplurality of target subscriber units. The call processing unit thendetermines whether at least one of the target subscriber unit isassigned thereto, and if so accesses the current routing informationpertaining to such target subscriber unit(s). Using the current routinginformation pertaining to such target subscriber unit(s), the callprocessing unit pages the target subscriber unit. If the call processingunit receives a response to the page, it establishes a dispatchcommunications link across the intra-area communications network toallow the calling subscriber unit to communicate with such targetsubscriber unit(s). If the call processing unit does not receive aresponse to the page, it sends a message to the calling subscriber unitindicating that such target subscriber unit(s) is not available.

If the call processing unit determines that it is not assigned to handledispatch calls for at least one of the target subscriber units, the callprocessing unit sends a request to a home location registration dispatch(HLR-D) device for information regarding the call processing unitassigned to handle calls for the target subscriber unit(s). Once thecall processing unit obtains that information, it sends a request to thetarget call processing unit(s) for the routing information pertaining tothe target subscriber unit(s). Having this information, the callprocessing unit pages the target subscriber unit(s). If the callprocessing unit receives any response to the page(s), it establishes adispatch communications link across the inter-area communicationsnetwork to allow the calling subscriber unit to communicate with suchtarget subscriber unit(s). If the call processing unit does not receivea response to the page(s), it sends a message to the calling subscriberunit indicating that such target subscriber unit(s) is not available.

Other aspects of the dispatch communications system include an HLR-Ddevice containing information related to subscribers, fleets, talkgroups, and current registrations; interfaces, such as dispatch sitecontrollers (DSCs), for respectively coupling the intra-areacommunication networks with the inter-area communications network;packet duplicators for generating voice packets for transmission acrossthe inter-area and/or intra-area communications networks; and cell citesincluding access controller gateways (ACGs) and enhanced basetransceiver stations (EBTSs).

Other aspects, features, and techniques of the invention will beapparent to one skilled in the relevant art in view of the followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an exemplary dispatchcommunications system in accordance with an embodiment of the invention;

FIG. 2 illustrates a flow diagram of an exemplary method of registeringa subscriber unit (SU) with the exemplary dispatch communications systemin accordance with another embodiment of the invention;

FIGS. 3-1 and 3-2 illustrate a flow diagram of an exemplary method ofprocessing a group dispatch call performed by the exemplary dispatchcommunications system in accordance with another embodiment of theinvention;

FIG. 4 illustrates a flow diagram of an exemplary method of tracking aroaming SU performed by the exemplary dispatch communications system inaccordance with another embodiment of the invention;

FIG. 5A illustrates a block diagram of an exemplary home locationregistration dispatch (HLR-D) device in accordance with anotherembodiment of the invention;

FIG. 5B illustrates a flow diagram of an exemplary method of registeringan SU performed by the HLR-D device in accordance with anotherembodiment of the invention;

FIG. 5C illustrates a flow diagram of an exemplary method of assistingin the processing of a group dispatch call performed by the HLR-D devicein accordance with another embodiment of the invention;

FIG. 6A illustrates a block diagram of an exemplary visitor locationregistration dispatch (VLR-D) device in accordance with anotherembodiment of the invention;

FIG. 6B illustrates a flow diagram of an exemplary method of processingof a group dispatch call performed by the VLR-D device in accordancewith another embodiment of the invention;

FIG. 6C illustrates a flow diagram of an exemplary method of assistingin the processing of a group dispatch call performed by the VLR-D devicein accordance with another embodiment of the invention;

FIG. 6D illustrates a flow diagram of an exemplary method of tracking aroaming SU performed by the VLR-D device in accordance with anotherembodiment of the invention; and

FIG. 6E illustrates a flow diagram of an exemplary method of assistingin the registration of an SU performed by the VLR-D device in accordancewith another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a block diagram of an exemplary dispatchcommunications system 100 in accordance with an embodiment of theinvention. The dispatch communications system 100 includes one or morehome location registration dispatch (HLR-D) devices 102 and 104, aninter-area communications network 106, a plurality of visitor homelocation registration dispatch (VLR-D) devices 108, 110, 112, and 114, aplurality of dispatch site controllers (DSCs) 118, 120, 122, 124, 126,and 128, a plurality of intra-area communications networks 130 and 132,a plurality of intra-area packet duplicators 136 and 138, a plurality ofinter-area (network) packet duplicators 134 and 140, a plurality ofaccess controller gateways (ACGs)/enhanced base transceiver stations(EBTSs) 142, 144, 146 and 148, and a plurality of subscriber units (SUs)150, 152, 160 and 162, which can be mobile stations (MSs), for example.

As is discussed in more detail below, the HLR-D devices 102 and 104 sendinformation to requesting elements of the dispatch communications system100, assist in the registration of SUs, and assist in the processing ofgroup dispatch calls. Each HLR-D includes a database containingprovisioning information for subscribers, fleets, talk-groups, andvarious elements of the dispatch communications system 100.

As is discussed in more detail below, the VLR-D devices 108, 110, 112,and 114 act as call processing units to process group dispatch calls,assist in the processing of group dispatch calls, and assist in trackingthe movement of SUs between different dispatch location areas (DLAs).Each VLR-D device includes a database containing information related toa portion of the active subscribers of the dispatch communicationssystem 100, and information related to group dispatch calls.

The inter-area communications network 106 facilitates voice and datacommunications between various elements of the dispatch communicationssystem 100, including the HLR-D devices 102 and 104, the VLR-D devices108, 110, 112, and 114, the DSCs 118, 120, 122, 124, 126, and 128, andthe inter-area (network) packet duplicators 134 and 140. The inter-areacommunications network 106 may be partitioned into multiple distinctnetworks, such as a network to assist in data communications betweenHLR-D and VLR-D devices, and another network to assist in voice and datacommunications between the VLR-D devices, DSCs, and inter-area packetduplicators. The inter-area communications network 106 may be of anysuitable types, including internet protocol (IP), asynchronous transfermode (ATM), and frame relay.

The DSCs 118, 120, and 122 provide an interface between the intra-areacommunications network 130 and the inter-area communications network106. In performing its interface function, the DSCs convert datacommunications between the protocol used in the intra-area network 130and the protocol used in the inter-area network 106. In addition, theDSCs provide an address mapping of the devices of the intra-areacommunications network 130 to the VLR-Ds, and vice-versa. In thismanner, a VLR-D is able to communicate with cell sites and other devicesof the intra-area communications network 130, and vice-versa. Forexample, a VLR-D will track the dispatch location area (DLA) of asubscriber, and then tell the corresponding DSC which DLA to use inpaging the subscriber. The DLA will then map the paging message from theVLR-D to the DLA. In addition, the DSCs 118, 120, and 122 also identifyappropriate links (e.g. a data link call identifier (DLCI)—Frame Relaytype network) or address (IP or ATM type network) information for groupdispatch calls spanning the intra-area network 130.

Similarly, the DSCs 124, 126, and 128 provide an interface between theintra-area communications network 132 and the inter-area communicationsnetwork 106. In performing its interface function, the DSCs convert datacommunications between the protocol used in the intra-area network 132and the protocol used in the inter-area network 106. In addition, theDSCs provide an address mapping of the devices of the intra-areacommunications network 132 to the VLR-Ds, and vice-versa. In thismanner, a VLR-D is able to communicate with cell sites and other devicesof the intra-area communications network 132, and vice-versa. Inaddition, the DSCs 124, 126, and 128 also identify appropriate data linkcall identifiers (DLCIs) for group dispatch calls spanning a Frame-Relaytype intra-area network 132.

The intra-area communications network 130 facilitates voice and datacommunications between the various elements serving a first distinctgeographical area 170 (e.g., Chicago), including the DSCs 118, 120, and122, the ACGs/EBTSs 142 and 144, and the packet duplicators 134, 136,and 138. Similarly, the intra-area communications network 132facilitates voice and data communications between the various elementsserving a second distinct geographical area 180 (e.g. Los Angeles),including the DSCs 124, 126, and 128, the ACGs/EBTSs 146 and 148, andthe packet duplicator 140. The intra-area networks 130 and 132 may be ofany suitable types, such as a Frame Relay. The geographic coverage ornumber of ACGs/EBTSs within a distinct geographical area such as 170 or180 may be arbitrarily small and need contain no more than one ACG/EBTSand one DSC. The geographic coverage or number of ACGs/EBTSs may be aslarge as is practical given the physical constraints of the DSC andintra-area Frame Relay Network (130,132).

The packet duplicators 134, 136, and 138 generate voice packets for SUslocated within the first geographical area 170. Some of the packetduplicators, such as 136 and 138, may operate to generate and send voicepackets only across the intra-area network 130. This may be the casewhere two or more SUs are both situated within geographical area 170.The other packet duplicator 134 may operate to generate and send voicepackets across the inter-area network 106. This may be the case wheretwo or more SUs are respectively situated in distinct geographical areas170 and 180. Similarly, packet duplicator 140 may operate to generateand send voice packets for transmission by SUs located within the secondgeographical area 180. The packet duplicator 140 may generate voicepackets compliant for transmission across both the intra-area network132 and the inter-area network 106.

The ACGs/EBTSs 142 and 144 are the represented cell sites that servicesubscribers, such as SUs 150 and 152, within the geographical area 170.Similarly, ACGs/EBTSs 146 and 148 are the represented cell sites thatservice subscribers, such as SUs 160 and 162, within the geographicalarea 180. The ACGs/EBTSs provide the wireless radio frequency (RF)interface and communications control between the SU's and thecorresponding intra-area networks.

As the functionality of the various elements of the dispatchcommunications system 100 has been discussed, the following provides adiscussion of an exemplary method of registering an SU, an exemplarymethod of processing a group dispatch call between three or more SUs,and an exemplary method of tracking the movement of an SU betweendistinct DLAs.

FIG. 2 illustrates a flow diagram of an exemplary method 200 ofregistering a subscriber unit (SU) with the exemplary dispatchcommunications system 100 in accordance with another embodiment of theinvention. In this example, SU 150 is making a request to register withthe dispatch communications system 100 to obtain dispatch call services.With further reference to FIG. 1, the registration method 200 begins byan SU 150 sending a registration request to the DSC 120 by way of theACG/EBTS 142 and the intra-area network 130 (block 202). Theregistration request may include information related to the subscriber,such as its international mobile station identifier (IMSI) or itsinternational mobile equipment identifier (IMEI). The DSC 120, in turn,sends the registration request to the HLR-D device 102 by way of theinter-area network 106 (block 204).

After receiving the registration request, the HLR-D device 102 searchesits database to determine whether the requesting SU 150 is provisioned(i.e., valid) for receiving dispatch call services (block 206). This mayentail the HLR-D device 102 searching its accounts/receivableinformation related to the subscriber to determine whether thesubscriber has paid for dispatch services. If the HLR-D device validatesthe requesting SU 150, the HLR-D device 102 assigns a preferred VLR-Ddevice (e.g., VLR-D device 110) to handle dispatch calls for therequesting SU 150 (block 208). The assignment of the VLR-D device 110may be based on the current registration of other members of therequesting subscriber's fleet and/or talk-group. In other words, it ispreferable that members of a fleet and/or talk group be assigned to thesame VLR-D device for call processing efficiency.

After assigning a preferred VLR-D device 110 to the requesting SU 150,the HLR-D device 102 sends the assignment to the VLR-D device 110 by wayof the inter-area network 106 (block 210). The VLR-D device 110 storesrouting information pertaining to the requesting SU 150, such as the DSCand DLA used for communicating with the SU 150. After receiving andprocessing the assignment of the requesting SU 150, the VLR-D device 110sends a registration acceptance message to the corresponding DSC 120 byway of the inter-area network 106 (block 212). The DSC 120, in turn,stores the VLR-D relationship for the SU 150 and sends a registrationacceptance message to the SU 150 by way of the intra-area network 130and corresponding ACG/EBTS 142 (block 214). Once the registrationprocess is complete, the SU 150 is now provisioned with the dispatchcommunications system 100 to make group dispatch calls to other SUs.

FIGS. 3-1 and 3-2 illustrate a flow diagram of an exemplary method 300of processing a group dispatch call by the exemplary dispatchcommunications system 100 in accordance with another embodiment of theinvention. In this example, SU 150 is making a group dispatch call to SU152 (e.g., another member of the same fleet and located in geographicalarea 170) and SUs 160 and 162 (e.g., subscribers located in geographicalarea 180). With further reference to FIG. 1, the group call processingmethod 300 begins with SU 150 sending a group call request message tothe DSC 120 by way of the corresponding ACG/EBTS 142 and the intra-areanetwork 130 (block 302). The group call request message includes theIMSI of SU 150 (i.e., the calling SU) and a talk-group identifier toidentify a talk-group comprised of SUs 152, 160, and 162 (i.e., thetarget SUs). The DSC 120 then sends the group call request message tothe VLR-D device 110 assigned to the SU 150 (block 304).

After the VLR-D 110 receives the group call request message, it searchesits database to determine whether it is assigned to handle dispatchcalls for the talk-group's target SUs (block 306). In such case, theVLR-D device 110 would have the routing information pertaining to thetarget SU. If it does, as in the case of SU 152, then the methodproceeds to block 314. In the case of target SUs not assigned to VLR-Ddevice 110, such as SUs 160 and 162, the VLR-D device 110 sends amessage to the HLR-D device 102 by way of the inter-area network 106requesting the information of the VLR-D device(s) assigned to the targetSUs 160 and 162 (block 308). The HLR-D device 102 responds by performinga database search and then sending the requested VLR-D deviceinformation to the VLR-D 110 by way of the inter-area network 106 (block310). In this example, VLR-D device 112 is assigned to the target SU 160and VLR-D device 114 is assigned to SU 162.

Once the VLR-D device 110 has information of the VLR-Ds 112 and 114respectively assigned to the target SUs 160 and 162, the VLR-D device110 sends respective messages to VLR-Ds 112 and 114 by way of theinter-area network 106 requesting the current routing informationpertaining to the target SUs 160 and 162, respectively, such as the DSCsand DLAs of the target SUs 160 and 162 (block 312). The VLR-D devices112 and 114 respectively perform database searches and then sends thecurrent routing information pertaining to the target SUs 160 and 162 tothe VLR-D device 110 (block 313).

Once the VLR-D device 110 has the routing information pertaining to thetarget SUs 150, 160 and 162, the VLR-D device 110 sends paging messagesto the target SUs 150, 160 and 162, respectively (block 314). In thecase of target SU 152, the VLR-D device 110 sends the paging message toSU 152 by way of the inter-area network 106, the DSC 120, the intra-areanetwork 130, and the ACG/EBTS 144. In the case of target SUs 160 and162, the VLR-D 110 device sends paging messages to SUs 160 and 162 byway of inter-area network 106, the DSCs 126 and 128, the intra-areanetwork 132, and the ACG/EBTS 146 and 148, respectively.

Subsequent to the transmission of the paging messages, the VLR-D device110 waits a predetermined time interval to determine whether anyresponses to the paging message have been received (block 316). If noresponse to the paging messages is received, the VLR-D device 110 sendsa message to the calling SU 150 by way of the inter-area network 106,the DSC 120, the intra-area network 130, and the ACG/EBTS 142 indicatingthat the target SUs are not available (block 318). If such is the case,the group call processing ends.

On the other hand, if the VLR-D device 110 receives any response to thepaging messages indicating that at least one of the target SUs isavailable, the VLR-D device 110 allocates channel resources so that thecalling and target SUs can perform dispatch communications with eachother (block 320). This may entail the VLR-D device 110 assigningrespective packet duplicators for the calling and target SUs, assigninga global call identifier to identify the group call, and assigning anappropriate addresses and data link call identifiers to identify path(s)through the inter-area network 106 and intraurban networks 130 and 132.If the dispatch call is only between SU 150 and SU 152 (because SUs 160and 162 are not available), the VLR-D device 110 instructs the DSC 120to assign the Global Call Identifier and utilize the appropriate DLCIfor the dispatch call through the intra-area network 130.

During the group dispatch call between the calling and target SUs, theVLR-D device 110 controls the communications between both parties (block322). Since a dispatch call is half-duplex, the VLR-D device 110 limitsthe channel to a single party after receiving a beginning oftransmission (BOT) signal from a “talking” SU. Then, opens the channelafter receiving an end of transmission (EOT) signal from the “talking”SU, thereby allowing the other SU to begin transmission.

During a group dispatch call, the VLR-D device 110 clears the call ifthere is no activity on the channel after a predetermined time intervalhas expired (block 324). To this endeavor, the VLR-D device 110 resets atimer each time it receives an EOT signal. If the VLR-D device 110receives a BOT signal prior to the expiration of the predetermined timeinterval, the VLR-D device 110 does not clear the call. However, if thepredetermined time interval expires, the VLR-D device 110 clears thecall, and sends messages to that effect to the corresponding packetduplicators and DSCs. After the call clears, the VLR-D 110 creates andstores in its database a detailed record of the call for billing and/orother purposes (block 326). Once this occurs, the call processing ends.

FIG. 4 illustrates a flow diagram of an exemplary method 400 of trackinga roaming SU by the exemplary dispatch communications system 100 inaccordance with another embodiment of the invention. In this example,the tracking of SU 162 is illustrated. With further reference to FIG. 1,according to the tracking method 400, the SU 162 detects that it hasroamed to a location covered by a different predefined group of cellcites also known as a dispatch location area (DLA) (block 402). The SU162 makes this determination by monitoring the strengths of the signalsreceived from proximate cells cites and utilizes procedures forselecting to a neighbor cell to maintain good coverage.

Once the SU 162 has detected it has roamed to a different DLA, it sendsa registration renewal request message to its assigned VLR-D device(e.g., VLR-D device 112) by way of the corresponding ACG/EBTS, theintra-area network 132, the DSC 128, and the inter-area network 106(block 404). Once the VLR-D device 112 receives the request, it updatesits database to denote the new DLA in which the SU 162 resides (block406). Then, the VLR-D device 112 sends an acknowledge message back tothe SU 162 by way of the inter-area network 106, DSC 128, intra-areanetwork 132, and corresponding ACG/EBTS (block 408). In such process,the corresponding DSC 128 may also note the change in the DLA of SU 162.

FIG. 5A illustrates a block diagram of an exemplary HLR-D device 500 inaccordance with another embodiment of the invention. The HLR-D 500 is anexemplary detailed version of at least one of the HLR-Ds 102 and 104shown in FIG. 1. The HLR-D 500 comprises a processor 502, an inter-areanetwork interface 504, and a memory 506. The processor 502 performs thevarious operations of the HLR-D, such as providing information torequesting elements such as during a group call processing event, andassisting in the SU registration process. The inter-area networkinterface 504 provides an interface to an inter-area network forcommunicating with other elements of a dispatch communications system.The memory 506, serving generally as a computer-readable medium, storesone or more software modules for controlling the operations of theprocessor 502, subscriber information, fleet and talk-group information,and current registration information.

FIG. 5B illustrates a flow diagram of an exemplary method 510 ofregistering an SU by the HLR-D device 500 in accordance with anotherembodiment of the invention. According to the method 510, the processor502 receives a registration request from an SU by way of the inter-areanetwork interface 504 (block 512). The processor 502 then searches thesubscriber information stored in memory 506 (block 514) to determinewhether the requesting SU is provisioned for receiving dispatch services(block 516).

If the processor 502 determines that the requesting SU is notprovisioned for receiving dispatch services, the processor 502 sends amessage to the SU by way of the inter-area network interface 504indicating that the SU is not valid for receiving dispatch services(block 518). Otherwise, the processor 502 assigns a preferred VLR-D forthe requesting SU based on the fleet and/or talk-group in which the SUbelongs (block 520). Then, the processor 502 sends a message to thepreferred VLR-D by way of the inter-area network interface 504indicating an assignment of the requesting SU to the preferred VLR-D(block 522).

FIG. 5C illustrates a flow diagram of an exemplary method 530 ofassisting in the processing of a group dispatch call by the HLR-D device500 in accordance with another embodiment of the invention. According tothe method 530, the processor 502 receives a request for the identity ofone or more VLR-Ds devices assigned to the target SU(s) by way of theinter-area network interface 504 (block 532). The processor 502 thensearches its database stored in memory 506 (block 534) to determinewhether the target SU(s) are provisioned to receive dispatch services(block 536).

If the processor 502 determines that at least one of the target SU(s)are not provisioned, it sends a message to the requesting networkelement by way of the inter-area network interface 504 indicating thatsuch target SU(s) are not provisioned to receive dispatch services(block 542). For those SU(s) that are provisioned, the processor 502searches the subscriber information stored in memory 506 to determinethe VLR-D device(s) assigned to the target SU(s) (block 538). Then theprocessor 502 sends information of the VLR-D device(s) assigned to thetarget SU(s) to the requesting network element by way of the inter-areanetwork interface 504 (block 540).

FIG. 6A illustrates a block diagram of an exemplary VLR-D device 600 inaccordance with another embodiment of the invention. The VLR-D 600 is anexemplary detailed version of at least one of the VLR-D devices 108,110, 112, and 114 shown in FIG. 1. The VLR-D 600 includes a processor602, an inter-area network interface 604, and a memory 606. Theprocessor 602 performs the various operations of the VLR-D device 600,such as group dispatch call processing, assisting in group dispatch callprocessing, and tracking movement of SUs between different DLAs. Theinter-area network interface 604 provides an interface to an inter-areanetwork for communicating with other elements of a dispatchcommunications system. The memory 606, serving generally as acomputer-readable medium, stores one or more software modules forcontrolling the operations of the processor 602, active subscriberinformation, global call identifiers, current call status, and calldetail information.

FIG. 6B illustrates a flow diagram of an exemplary method 610 ofprocessing a group dispatch call by the VLR-D device 600 in accordancewith another embodiment of the invention. According to the callprocessing method 610, the processor 602 receives a group call requestfrom a calling SU by way of the inter-area network interface 604 (block612). The group call request includes information on the targettalk-group including two or more target SUs. Then, the processor 602searches the subscriber information stored in the memory 606 (block 613)to determine whether any of the target SUs are assigned to the instantVLR-D 600 (block 614).

If the processor 602 determines that at least one of the target SUs areassigned to the instant VLR-D 600, the call processing method 600proceeds to block 624 for those target SU(s) assigned to VLR-D 600. Forthose target SU(s) not assigned to VLR-D 600, the processor 602 sends amessage to an HLR-D device by way of the inter-area network interface604 requesting information regarding the VLR-D device(s) assigned to thetarget SU(s) (block 616). Following the request, the processor 602receives a response from the HLR-D device by way of the inter-areanetwork interface 604 (block 618). The processor 602 then analyzes theresponse (block 620). If the response received from the HLR-D deviceindicates that at least one of the target SU(s) is not provisioned toreceive dispatch services, the processor 602 sends a message indicatingthe same to the calling SU by way of the inter-area network interface604 (block 621).

Otherwise, if the response received from the HLR-D device providesinformation regarding the VLR-D device(s) assigned to the target SU, theprocessor 602 sends a request to such VLR-D device(s) by way of theinter-area network interface 604 for the target SU(s) routinginformation, such as the DSC and DLA of the target SU(s) (block 622).After receiving such information from the target VLR-D devices, theprocessor 602 sends paging message(s) directed at the DSC and DIA of thetarget SU(s) by way of the inter-area network interface 604 (block 624).The processor 602 then determines whether it has received any responsesto the paging message(s) (block 626). If the processor 602 does notreceive any response to the page(s) within a predetermined time intervalafter sending the page, the processor 602 sends a message to the callingSU by way of the inter-area network interface 604 indicating that thetarget SU(s) are unavailable (block 628).

Otherwise, the processor 602 allocates channel resources and controlsthe dispatch communications between the calling and target SUs (block630). With regard to setting up the group dispatch call, the processor602 generates a global call identifier to identify the group dispatchcall, assigns packet duplicators to generate the voice packets for thecalling and target SUs, and identifies appropriate link or addressinformation if the group dispatch call traverses the inter-areacommunications network 106. With regard to controlling the dispatchcommunications, the processor 602 monitors the BOT signals from SUs tolimit the channel exclusively to a single SU and monitors the EOTsignals from SUs to open the channel. The processor 602 clears the callif a predetermined time interval has lapsed since the last EOT signal(block 632). Then, the processor 602 creates a call detail record andstores it in memory 606 (block 634).

FIG. 6C illustrates a flow diagram of an exemplary method 650 ofassisting in the processing of a dispatch call by the VLR-D device 600in accordance with another embodiment of the invention. This is the casewhere the VLR-D device 600 is assigned to at least one of the targetSUs, and is assisting the VLR-D of the calling SU with the processing ofthe dispatch call. According to the method 650, the processor 602receives a request message for routing information pertaining to atleast one target SU(s) by way of the inter-area network interface 604(block 652). Once receiving the request, the processor 602 searches thesubscriber information stored in the memory 654 to obtain the routinginformation (e.g. the DSC and DLA) pertaining to the target SU(s) (block654). Then, the processor 602 sends this information to the requestingVLR-D device by way of the inter-area network interface 604 (block 656).

FIG. 6D illustrates a flow diagram of an exemplary method 660 oftracking a roaming SU by the VLR-D device 600 in accordance with anotherembodiment of the invention. This example illustrates the tracking of anSU when it roams between different DLAs. According to the method 660,the processor 602 receives a request for a renewal registration from aroaming SU by way of the inter-area network interface 604 (block 662).In response to the request, the processor 602 updates the subscriberinformation stored in the memory 606 to reflect that the SU has roamedto a new DLA (block 664). Then, the processor 602 sends a message to theSU by way of the inter-area network interface 604 acknowledging theupdated status of the current DLA of the SU (block 666).

FIG. 6E illustrates a flow diagram of an exemplary method 670 ofassisting in the registration of an SU performed by the VLR-D 600 inaccordance with another embodiment of the invention. This exampleillustrates the process of the VLR-D device obtaining an assignment of aregistering SU from an HLR-D. According to the method 670, the processor602 receives a message from an HLR-D device by way of the inter-areanetwork interface 604 assigning the VLR-D device 600 to handle dispatchcalls for a registering SU (block 672). The assignment may includerouting information pertaining to the SU, such as its DSC and DLA. Thenthe processor 602 updates the subscriber information stored in memory606 to include the routing information pertaining to the SU (block 674).Once the updating is complete, the processor 602 sends a message to theregistering SU by way of the inter-area network interface 604 indicatingthat the registration process is complete (block 676).

While the invention has been described in connection with variousembodiments, it will be understood that the invention is capable offurther modifications. This application is intended to cover anyvariations, uses or adaptation of the invention following, in general,the principles of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

1. A dispatch communications system, comprising: a first intra-areadispatch communications network to facilitate group dispatch callingbetween subscriber units residing within a first geographical area; asecond intra-area dispatch communications network to facilitate groupdispatch calling between subscriber units residing within a secondgeographical area different than said first geographical area; aninter-area dispatch communications network to facilitate group dispatchcalling between subscriber units residing respectively in said first andsecond geographical areas; and a first interface device for interfacingsaid first intra-area dispatch communications network to said inter-areadispatch communications network by converting communications between aprotocol of the first intra-area dispatch communications network and theinter-area dispatch communications network.
 2. The dispatchcommunications system of claim 1, further comprising a first callprocessing unit for establishing a dispatch communications link acrosssaid inter-area dispatch communications network.
 3. The dispatchcommunications system of claim 2, wherein said first call processingunit is configured to: receive a group dispatch call request from acalling subscriber unit residing in said first geographical area,wherein the dispatch call request identifies at least one targetsubscriber unit residing in said second geographical area; and establishsaid dispatch communications link across said inter-area communicationslink to allow said calling subscriber unit to communicate with said atleast one target subscriber unit.
 4. The dispatch communications systemof 3, further comprising a home location registration dispatch (HLR-D)device containing information related to call processing units assignedto process dispatch calls for subscriber units.
 5. The dispatchcommunications system of claim 4, wherein said first call processingunit is configured to: request and receive information from said HLR-Ddevice related to a second call processing unit assigned to handledispatch calls for said at least one target subscriber unit; request andreceive information from said second call processing unit related torouting information pertaining to said at least one target subscriberunit; and send at least one paging message in accordance with saidrouting information.
 6. The dispatch communications system of claim 5,wherein said first call processing unit is configured to establish saiddispatch communications link after receiving a response to said at leastone paging message from said at least one target subscriber unit.
 7. Thedispatch communications system of claim 5, wherein said first callprocessing unit is configured to send a message to said callingsubscriber unit indicating that said at least one target subscriber unitis unavailable if no response to said paging message is received fromsaid at least one target subscriber unit.
 8. The dispatch communicationssystem of claim 1, further comprising first and second packetduplicators for generating voice packets respectively for said callingsubscriber unit and said at least one target subscriber unit, whereinsaid voice packets are compliant for transmission across said inter-areacommunications network.
 9. The dispatch communications system of claim1, further comprising a second interface device for interfacing saidsecond intra-area communications network to said inter-areacommunications network, wherein the first interface device mapsaddresses of devices of the first intra-area communications network. 10.The dispatch communications system of claim 1, further comprising afirst set of cell sites coupled to said first intra-area communicationsnetwork, and a second set of cell sites coupled to said secondintra-area communications network.
 11. The dispatch communicationssystem of claim 1, further comprising a first packet duplicator forgenerating voice packets to be transmitted across said first intra-areacommunications network, and a second packet duplicator for generatingvoice packets to be transmitted across said second intra-areacommunications network.
 12. The dispatch communications system of claim1, wherein at least one of said subscriber units comprises a mobilestation.
 13. A method of processing a dispatch call, comprising:receiving a group dispatch call request from a calling subscriber unitby way of a first intra-area dispatch communications network configuredto facilitate group dispatch calling between subscriber units residingwithin a first geographical area, wherein the group dispatch callrequest identifies a talk-group including at least one target subscriberunit residing in a second geographical area distinct from said firstgeographical area, and wherein a second intra-area dispatchcommunications network is configured to facilitate group dispatchcalling between subscriber units within said second geographical area;establishing a dispatch communications link between said first andsecond intra-area dispatch communications networks via an inter-areacommunications network to allow said calling subscriber unit tocommunicate with said at least one target subscriber unit, if said atleast one target subscriber unit is available; and convertingcommunications between a protocol of the first intra-area dispatchcommunications network and the inter-area communications network. 14.The method of claim 13, further comprising requesting and receivinginformation from a home location registration dispatch (HLR-D) devicerelated to a call processing unit assigned to handle dispatch callingfor said at least one target subscriber unit.
 15. The method of claim14, further comprising requesting routing information pertaining to saidat least one target subscriber unit from said call processing unit. 16.The method of claim 15, further comprising sending at least one pagingmessage in accordance with said routing information pertaining to saidat least one target subscriber unit.
 17. The method of claim 16, whereinestablishing said dispatch communications link comprises establishingsaid dispatch communications link if a response to said at least onepaging message is received from said at least one target subscriberunit.
 18. The method of claim 16, further comprising sending a messageto said calling subscriber unit indicating that said at least one targetsubscriber unit is unavailable if no response to said paging message isreceived.
 19. The method of claim 13, wherein establishing said dispatchcommunications link comprises assigning first and second packetduplicators to generate voice packets respectively for said callingsubscriber unit and said at least one target subscriber unit, whereinsaid voice packets are compliant for transmission across said inter-areacommunications network.
 20. The method of claim 13, wherein said callingsubscriber unit and/or said at least one target subscriber unitcomprises a mobile station.
 21. A call processing unit, comprising: anetwork interface to interface with an inter-area dispatchcommunications network; and a processor configured to: receive a groupdispatch call request from a calling subscriber unit by way of saidnetwork interface, wherein said dispatch call request identifies atalk-group including a plurality of target subscriber units; sendrespective paging messages for said target subscriber units; establish adispatch communications link between said calling and at least one ofsaid target subscriber units across said inter-area dispatchcommunications network if a response to said paging message is receivedby way of said network interface; generate a data link call identifierfor identifying said dispatch communications link across said inter-areadispatch communications network.
 22. The call processing unit of claim21, wherein said processor is configured to: send a message to anothercall processing unit by way of said network interface requesting routinginformation pertaining to at least one of said target subscriber units;and receive said routing information pertaining to at least one of saidtarget subscriber unit by way of said network interface.
 23. The callprocessing unit of claim 22, wherein said processor is configured to:send a message to a home location registration dispatch (HLR-D) deviceby way of said network interface requesting information related to saidanother call processing unit; and receive said information related tosaid another call processing unit by way of said network interface. 24.The call processing unit of claim 21, wherein said processor isconfigured to receive an assignment to handle dispatch calls for asubscriber unit by way of said network interface.
 25. The callprocessing unit of claim 21, further comprising a memory, and whereinsaid processor is configured to: receive an assignment to handledispatch calls for a subscriber unit by way of said network interface;store information related to said assignment in said memory; and send amessage to said subscriber unit by way of said network interfaceindicating that the subscriber unit is registered to receive dispatchcalling services.
 26. The call processing unit of claim 21, furthercomprising a memory, and wherein said processor is configured to:receive routing information pertaining to a subscriber unit by way ofsaid network interface; and store said routing information in saidmemory.
 27. The call processing unit of claim 21, further comprising amemory to store a current dispatch location area of a subscriber unit,and wherein said processor is configured to: receive a message from saidsubscriber unit indicating that said subscriber unit is changing fromsaid current dispatch location area to a new dispatch location area; andupdate said information related to said current dispatch location areaof said subscriber unit to note said new dispatch location area of saidsubscriber unit.
 28. The call processing unit of claim 21, furthercomprising a memory containing routing information pertaining to anothersubscriber unit, wherein said processor is configured to: receive arequest from a requesting element for said routing informationpertaining to said another subscriber unit; access said routinginformation from said memory; and send said routing information to saidrequesting element by way of said network interface.
 29. The callprocessing unit of claim 21, wherein said processor is configured togenerate an assignment of packet duplicators for generating voicepackets respectively for said calling subscriber unit and at least oneof said target subscriber units.
 30. The call processing unit of claim21, wherein said processor is configured to generate a global callidentifier to identify said group dispatch call between said calling andat least one of said target subscriber units.
 31. The call processingunit of claim 21, wherein said calling subscriber unit and/or at leastone of said target subscriber unit comprises a mobile station.
 32. Acomputer-readable medium comprising one or more software modules tocontrol a processor to: receive a group dispatch call request from acalling subscriber unit by way of a network interface coupled to aninter-area dispatch communications network, wherein said group dispatchcall request identifies a talk-group including a plurality of targetsubscriber units; send respective paging messages in accordance withrouting information pertaining to said target subscriber units;establish a communications link between said calling subscriber unit andat least one of said target subscriber units across said inter-areadispatch communications network if a response to said paging message isreceived by way of said network; and generate a data link callidentifier for identifying said dispatch communications link across saidinter-area dispatch communications network.
 33. The computer-readablemedium of claim 32, wherein said one or more software modules controlsaid processor to: send a message to a call processing unit by way ofsaid network interface requesting routing information pertaining to atleast one of said target subscriber units; and receive said routinginformation by way of said network interface.
 34. The computer-readablemedium of claim 32, wherein said one or more software modules controlsaid processor to: send a request to a home location registrationdispatch (HLR-D) device by way of said network interface for informationrelated to said call processing unit; and receive said informationrelated to said call processing unit by way of said network interface.35. The computer-readable medium of claim 32, wherein said one or moresoftware modules control said processor to receive an assignment tohandle dispatch calls for said calling subscriber unit by way of saidnetwork interface.
 36. The computer-readable medium of claim 32, whereinsaid one or more software modules control said processor to: receive anassignment to handle dispatch calls for said calling subscriber unit byway of said network interface; store information related to saidassignment in said memory; and send a message to said calling subscriberunit by way of said network interface indicating that the callingsubscriber unit is registered to receive dispatch calling services. 37.The computer-readable medium of claim 32, wherein said one or moresoftware modules control said processor to: receive routing informationpertaining to said calling subscriber unit by way of said networkinterface; and store said routing information in said memory.
 38. Thecomputer-readable medium of claim 32, further comprising a memory tostore information related a current dispatch location area of asubscriber unit, and wherein said processor is configured to: receive amessage from said subscriber unit indicating that said subscriber unitis changing from said current dispatch location area to a new dispatchlocation area; and update said information related to said currentdispatch location area of said subscriber unit to note said new dispatchlocation area of said subscriber unit.
 39. The computer-readable mediumof claim 32, wherein said one or more software modules control saidprocessor to: receive a request from a requesting element for routinginformation pertaining to another subscriber unit; access said routinginformation from a memory; and send said routing information to saidrequesting element by way of said network interface.
 40. Thecomputer-readable medium of claim 32, wherein said one or more softwaremodules control said processor to generate an assignment of packetduplicators for generating voice packets respectively for said callingsubscriber unit and at least one of said target subscriber units. 41.The computer-readable medium of claim 32, wherein said one or moresoftware modules control said processor to generate a global callidentifier to identify said dispatch call between said callingsubscriber unit and at least one of said target subscriber units. 42.The computer-readable medium of claim 32, wherein said callingsubscriber unit and/or at least one of said target subscriber unitscomprises a mobile station.